1. Field
The present embodiments generally relate to systems and methods for adjusting the activity or selectivity of a catalyst. More particularly, embodiments of the present invention relate to systems and methods for selectively adjusting the activity or selectivity of a catalyst for hydrocarbon processing through an in-situ addition of one or more doping agents during regeneration of the catalyst.
2. Description of the Related Art
Hydrocarbon cracking is a method where under controlled temperature, pressure, and reaction conditions, one or more carbon-carbon bonds in a heavy molecular weight hydrocarbon can be broken (or “cracked”) to form two or more lower molecular weight hydrocarbons or rearranged, with or without hydrogen transfer, to different molecules, including olefinic and aromatic compounds. Generally temperature, pressure and residence time within the cracker are adjusted to favor the production of desirable compounds. In fluidized catalytic crackers (“FCC”), a catalyst is employed to increase the yield of preferred lower molecular weight hydrocarbons, and to compensate for variations in hydrocarbon feedstock composition. Various additives or doping agents can be added to the catalyst to provide a doped catalyst where high performance or highly selective catalysts are desired.
Traditional production of doped FCC catalysts involves a multi-step process where the catalyst and the doping agent are uniformly dispersed within a solution. Heat is often applied to the solution to precipitate the catalyst. While a uniform, highly porous catalyst can thus be produced, the doping agent is dispersed more-or-less uniformly throughout the catalyst particle. Alternatively, the solid catalyst is dispersed in a solution containing the doping agent and dried. Since cracking occurs only on the exposed surfaces of the catalyst particle (hence the desirability of a highly porous catalyst), doping agent embedded deep within the catalyst matrix is unavailable to the cracking process. Where the supply of doping agent is limited, or where the doping agents are expensive or environmentally sensitive, the quantity of doping agent “lost” within the catalyst matrix may limit the overall availability of catalyst, may dramatically increase the cost of fresh catalyst, or may dramatically increase the cost of disposal for spent catalyst.
Where the composition of an incoming hydrocarbon feedstock is highly variable, it may be desirable to adjust the doping agent type or concentration to maintain a consistent finished product. With a traditional catalyst, since the doping agent remains embedded within the catalyst matrix, changing catalysts and/or doping agents in response to feedstock variations often requires complete replacement of the catalyst charge in the system. Such replacements are inefficient and costly, particularly as the variability of hydrocarbon feedstocks increases due to the frequent sourcing from multiple production regions scattered across wide geographic areas.
Given increasing reliance on the cracking of marginal quality crude oil feedstocks having highly variable compositions, there is a need therefore, for a method and process for rapidly adjusting the quantity or composition of doping agents used in FCC catalysts.